I am never in this thread Andrea, but I saw your question and I have something like an answer.

All the books ARE about Narnia. The history (Chronicles) of Narnia. I think the best thing is if you read them all. They are not very hard to read and I am pretty sure you will love them! You can start with

your book 2, then, 4 and then 5. Book five is the upcoming third movie.

After that, read, The Silver Chair, The Horse And His Boy, The Magicians Nephew, and last, The Last Battle.

That, I think, its the order in which the books were published. But you can read them any way you want.

Really, there is too much in them to explain here. It would be a very, very long post.

You can go to the following thread and read what I wrote (and others) about how to read the books: